On Thu, Jul 13, 2023 at 08:02:27AM +0530, Kumar Kartikeya Dwivedi wrote:
> The plumbing for offline unwinding when we throw an exception in
> programs would require walking the stack, hence introduce a new
> arch_bpf_stack_walk function. This is provided when the JIT supports
> exceptions, i.e. bpf_jit_supports_exceptions is true. The arch-specific
> code is really minimal, hence it should straightforward to extend this
> support to other architectures as well, as it reuses the logic of
> arch_stack_walk, but allowing access to unwind_state data.
>
> Once the stack pointer and frame pointer are known for the main subprog
> during the unwinding, we know the stack layout and location of any
> callee-saved registers which must be restored before we return back to
> the kernel.
>
> This handling will be added in the next patch.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> arch/x86/net/bpf_jit_comp.c | 21 +++++++++++++++++++++
> include/linux/filter.h | 2 ++
> kernel/bpf/core.c | 9 +++++++++
> 3 files changed, 32 insertions(+)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index 438adb695daa..d326503ce242 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -16,6 +16,7 @@
> #include <asm/set_memory.h>
> #include <asm/nospec-branch.h>
> #include <asm/text-patching.h>
> +#include <asm/unwind.h>
>
> static u8 *emit_code(u8 *ptr, u32 bytes, unsigned int len)
> {
> @@ -2660,3 +2661,23 @@ void bpf_jit_free(struct bpf_prog *prog)
>
> bpf_prog_unlock_free(prog);
> }
> +
> +bool bpf_jit_supports_exceptions(void)
> +{
> + return IS_ENABLED(CONFIG_UNWINDER_ORC) || IS_ENABLED(CONFIG_UNWINDER_FRAME_POINTER);
> +}
> +
> +void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie)
> +{
> +#if defined(CONFIG_UNWINDER_ORC) || defined(CONFIG_UNWINDER_FRAME_POINTER)
> + struct unwind_state state;
> + unsigned long addr;
> +
> + for (unwind_start(&state, current, NULL, NULL); !unwind_done(&state);
> + unwind_next_frame(&state)) {
> + addr = unwind_get_return_address(&state);
I think these steps will work even with UNWINDER_GUESS.
What is the reason for #ifdef ?
> + if (!addr || !consume_fn(cookie, (u64)addr, (u64)state.sp, (u64)state.bp))
> + break;
> + }
> +#endif
> +}
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index f69114083ec7..21ac801330bb 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -920,6 +920,8 @@ bool bpf_jit_needs_zext(void);
> bool bpf_jit_supports_subprog_tailcalls(void);
> bool bpf_jit_supports_kfunc_call(void);
> bool bpf_jit_supports_far_kfunc_call(void);
> +bool bpf_jit_supports_exceptions(void);
> +void arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie);
> bool bpf_helper_changes_pkt_data(void *func);
>
> static inline bool bpf_dump_raw_ok(const struct cred *cred)
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index 5c484b2bc3d6..5e224cf0ec27 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -2770,6 +2770,15 @@ int __weak bpf_arch_text_invalidate(void *dst, size_t len)
> return -ENOTSUPP;
> }
>
> +bool __weak bpf_jit_supports_exceptions(void)
> +{
> + return false;
> +}
> +
> +void __weak arch_bpf_stack_walk(bool (*consume_fn)(void *cookie, u64 ip, u64 sp, u64 bp), void *cookie)
> +{
> +}
> +
> #ifdef CONFIG_BPF_SYSCALL
> static int __init bpf_global_ma_init(void)
> {
> --
> 2.40.1
>
